DESCRIPTION: (Investigator's Abstract) The proposed research will investigate the anatomy, physiology and effects on visually guided behavior of inputs from the retina and nucleus isthmi on a central visual processing area, the optic tectum. The isthmotectal network of the leopard frog will be used as a model vertebrate system. The specific aims are as follows: 1) To determine the retinal distribution of retinotectal ganglion cells after optic chiasm hemisections. Such hemisections spare visually guided prey catching and horseradish peroxidase histochemistry will be used to determine if there are regions of the tectum deafferented of retinal input. 2) To study possible behavioral and physiological changes after optic chiasm hemisection. Using both behavioral tests and single unit extracellular tectal recording, hemisected and matched controls will be compared. 3) To investigate changes in visually guided behavior after bilateral n. isthmi ablation. Animals will be tested to determine if visual deficits are global or primarily restricted to monocular visual fields. 4) To study the synaptic anatomy of horseradish peroxidase labeled isthmotectal and tectoisthmal axons. Electron microscopy will be used to determine the elements that are in synaptic contact with terminals of these axons. The long term objective of this study is to determine how visual information is processed in the central nervous system in order to further our understanding of vision.